This kind of jet engine generally comprises from the upstream end to the downstream end in the direction of flow of the gases a fan, one or more compression stages, for example a low-pressure compressor and a high-pressure compressor, a combustion chamber, one or more turbine stages, for example a high-pressure turbine and a low-pressure turbine, and a gas exhaust pipe. To each compressor there may correspond a turbine, the two being connected by a part, thus forming a high-pressure body and a low-pressure body, for example.
The jet engine has at the upstream end and at the downstream end bearing enclosures containing rolling bearing and gear members lubricated with oil. Oil thrown off by these rotating parts forms a mist (or suspension) of droplets in suspension in the corresponding volume of the enclosures. Moreover, a flow of gas (air) passes through them, notably for ventilation purposes.
The upstream and downstream enclosures are formed and delimited by walls of the fixed structure of the jet engine and also by walls of rotary elements. They must allow the passage of a flow of gas but must retain as much oil as possible inside them, which is why the seal between the fixed elements and the rotary elements of an oil enclosure is a particularly difficult problem.
In a known manner, sealing is provided by means of labyrinth seals, i.e. seals formed by lips fastened to a rotary part and an abradable material fastened to a fixed part facing the lips. A clearance is maintained between these lips and the fixed part to allow the passage of a flow of gas coming from the low-pressure or high-pressure compressors; these gases oppose the exit of oil via the labyrinth seal; their flow rate is determined so as to be sufficient when idling and is therefore high in other flight phases (in which the flow rate of air aspirated by the fan of the jet engine is higher). This high flow in the other flight phases has at least two harmful consequences: firstly it commensurately reduces the efficiency of the engine and secondly it tends to entrain a greater quantity of air contaminated with oil to be treated by oil removers.
Replacing labyrinth seals with “brush” seals has therefore been envisaged, the latter including a plurality of juxtaposed substantially radial fibers fixed to a fixed part and the free ends of which are in contact with (or very close to) a rotary part, the fibers preferably being slightly inclined in the rotation direction of the rotary part; the fibers of the brush seal may be carbon fibers, for example.
Such brush seals have the advantage of requiring, to guarantee their oil-tightness, a flow of gas passing through them at a flow rate that is not excessive. However, the rubbing of the fibers on the track on the rotary part adapted to be in contact with their ends causes them to wear and thus also reduces their efficacy over time. Such wear is accentuated if there is an imbalance of the rotary part (the center of mass thereof not being on the rotation axis).
To alleviate this drawback, the document EP-0567392-B1 (of which the Applicant is the patentee) discloses a brush seal that comprises an annular brush body constituted of two flanges and mounted in the stator and fibers fixed by a first end into the brush body so as to be inclined relative to the axis of the rotary part and oriented toward the latter so that their second end is flush with the part to create a sealed curtain between the two annular volumes.
Moreover, the brush body is constituted of a plurality of ring sectors mounted in the stator, to allow slight automatic movement of the fibers away from the rotary part by becoming inclined relative to the axis of the part to allow eccentricity of the part relative to the stator (resulting from an imbalance, for example) at the same time as providing the seal between the two annular volumes.
In designing the brush body, each annular sector has a head at a first end that is mounted in a cylindrical groove of the stator.
The sectors are advantageously held in place by an elastic ring tensioned against a second end of the brush body opposite the head to hold the sectors of the brush body tightly together in a rest position in which the fibers have the smallest possible inclination relative to a radial plan of the axis of the rotary part.